Process for the preparation of difluoroamine



United States Patent 3,357,803 PROCESS FQR THE PREPARATION OF DIFLUOROAMINE Jeremiah P. Freeman, Huntsville, Ala., and Al Kennedy,

Fayetteville, Tenn., assignors to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware N0 Drawing. Filed Mar. 31, 1959, Ser. No. 803,325 Claims. (Cl. 23-356) This invention concerns a process for the preparation of difluoroamine (HNF by the reduction of tetrafluorohydrazine (N F It is reported in th early prior art that difluoroamine was produced by the electrolysis of ammonium bifiuoride. However, later investigators, attempting to reproduce the earlier art, have failed to produce difluoroamine and have questioned the certainty of the identification of difluoroamine by earlier investigators.

It has also been found that trace quantities of difluoroamine are produced in the reaction of nitrogen trifiuoride with arsenic at elevated temperatures. The main product is, however, tetrafluorohydrazine.

Direct fluorination of nitrogen-containing compounds, such as ammonia or urea, has also been tried as a method of producing difluoroamine. However, these methods of preparation are unsuitable because they not only give low yields, but the reaction products are complex mixtures from which the small amount of difluoroamine present can be extracted only with considerable difficulty.

An object of this invention is to provide processes which will produce a reaction mixture from which pure difluoroamine can be recovered with a minimum of work-up.

A further object of this invention is to provide processes which produce difluoroamine in good yields.

It has been found that tetrafluorohydrazine (N F is reduced to difluoroamine by reaction with reducing agents under mild reaction conditions.

Tetrafluorohydrazine is prepared by heating nitrogen trifluoride (NF at substantially atmospheric pressure and at a reaction temperature of from about 100 C. to about 500 C., preferably 375 C. to 450 C., in the presence of a catalytic metal surface, such as copper, arsenic, or stainless steel, to form tetrafluorohydrazine (N F When employing a reaction temperature in the range of 375 C. to 450 C., the contact time of the nitrogen trifiuoride with the catalytic metal surface should be about to minutes. The reaction mixture is condensed at low temperatures and the tetrafluorohydrazine is separated therefrom.

The nature of the reducing agents which will produce difluoroamine is varied. Thus, hydrogen will reduce tetrafluorohydrazine to produce some difluoroamine, but the reaction mixture is explosive under most conditions and nitrogen and hydrogen fluoride result from the explosive reaction. Thus, hydrogen is not a preferred reducing agent. Certain hydrides will also produce difluoroamine by the reduction of tetrafluorohydrazine, including arsine, stibine, and phosphine. Using arsine, yields of difluoroamine as high as 60% have been obtained. It has been observed, however, that under some conditions the reaction mixture containing arsine is explosive. Also, as is known, arsine, stibine, and phosphine are poisonous compounds. Furthermore, they are gases at room or higher temperatures and thus present some handling difiiculties. They do not represent preferred reducing agents.

Alkyl mercaptans in which the alkyl group contains from 1 to 6 carbon atoms overcome many of the objections of the hereinbefore described reducing agents. Under the prescribed reaction conditions, they do not produce explosive reaction mixtures, they are much higher 3,357,803 Patented Dec. 12, 1967 boiling, which facilitates handling, and they are much less poisonous than the hydrides set forth hereinbefore. Ethyl, butyl, pentyl, and hexyl mercaptans represent compounds of this class which are particularly suitable.

Aryl mercaptans, including thiophenol and alkyl substituted thiophenols, represent a preferred class of reducing agents. They thiophenols are a preferred class because they have the advantage of producing high yields of the desired product, do not cause the conversion of N F to nitrogen, and permit easier purification of the HNF produced. Furthermore, the mixtures are not explosive under the reaction conditions employed.

In general, it appears that any substance which will readily produce hydrogen atoms will function as a reducing agent for the reduction of N 11. Thus, in addition to the hereinbefore set forth reducing agents, aldehydes will also react with N F in the presence of catalytic quantities of peroxide to produce HNF The reaction temperatures employed will depend to some extent on the particular reducing agent used. Thus, the reduction of N 1 can be carried out at temperatures as low as room temperature, but the reaction rate is low. It is not preferred to carry out the reaction at temperatures below 30 C. An upper temperatur of about 70 C. applies to most reducing agents, there frequently being an explosive tendency above this temperature. A preferred range is from 45 C. to 60 C.

The reaction time is also dependent on the reactivity of the specific reducing agent being used. Thus arsine at 50 C. will give yields of difluoroamine up to 60% in one hour. Butyl mercaptan, as typical of the alkyl mercaptans which can be used, gives yields of the order of 35% to 40% in two hours at 50 to 60 C. Thiophenol, a preferred embodiment as hereinbefore set forth, requires much longer reaction times in order to obtain high yields. Thus, an initial reaction period of four hours at 50 to 55 0., followed by separation of the difluoroamine and recycle of the unconverted N F for an additional 4.5 hours at 50 to 55 C. produced yields in the 35 %to 50% range.

The reaction may be conducted at atmospheric pressure or at pressures slightly below or above atmospheric pressure. A preferred range is from about 0.7 to about 1.5 atmospheres.

The ratio of the reactants can also be varied over a wide range and still be within the scope of the invention. As might be expected, the optimum ratio will depend on such factors as the reactivity of the reducing agent being used, the reaction temperature employed, etc. Thus, in the cas of arsine at a reaction temperature of 50 to 55 C., a one to one molar ratio of arsine to tetrafluorohydrazine was found to be satisfactory. In the case of the alkyl and a1yl mercaptans, higher molar ratios of mercaptan to tetrafluorohydrazine were required for best results. Molar ratios of alkyl or aryl mercaptan to tetrafluorohydrazine of about five to one were found to be most satisfactory.

Since the reaction for the preparation of difluoroamine requires a reducing agent, the presence of oxygen is obviously undesirable. In addition N 1 reacts with oxygen. The reaction can be carried out in an inert atmosphere, such as nitrogen or helium.

Furthermore, the reaction proceeds best under substantially anhydrous conditions and, therefore, the reactants should be dried before using. Conventional desiccating methods may be employed, and the reaction mixture should be protected from moisture by means of Drierite traps, etc.

Difiuoroamine is a valuable oxidizer for rocket fuels because it can be handled as a liquid at room temperature, i.e. it is less cryogenic than other oxidizers, such as oxygen, fluorine and tetrafluorohydrazine. Furthermore,

it is a stable compound and can be stored for prolonged periods without any indication of decomposition. It is the first stable oxidizer of the NF type which is in the propellant energy range which can be stored as a liquid at room temperature.

As an example of the use of difluoroamine as a rocket fuel oxidizer, it can be used for the oxidation of hydrazine to produce nitrogen and hydrogen fluoride quantitatively. The calculated I (specific impulse) of the reaction of difluoroamine and hydrazine (at 600 p.s.i.) is 285, which means that it is a very high energy combination. Since the mixture of difluoroamine and hydrazine ignite on mixing, they must be stored separately when the mixture is to be used as a missile or rocket propellant. When the missile or rocket is to be fired, equivalent quantities of difluoroamine and hydrazine are metered by conventional means into a combustion chamber where they ignite. The thrust which results when the two liquids are converted into nitrogen and gaseous hydrogen fluoride propels the rocket.

The following examples set forth certain well-defined embodiments of the application of this invention. They are not, however, to be considered as limitations thereof, since many modifications may be made without departing from the spirit and scope of this invention.

Unless otherwise specified, all parts are parts by weight. All temperatures are centigr-ade unless otherwise noted.

EXAMPLE I Preparation of HNF from N F and thiophenol A 300 cc. steel bomb containing 178 cc. (0.0079 mole) of N F and 4 cc. (0.039 mole) of thiophenol was heated at 50 C. to 55 C. for four hours. The volatile products were then distilled through a bath at 130 C. and the material that passed through this bath was returned to the bomb. The retained fraction was purified by two distillations through the l30 C. bath and the material that passed through this bath was returned to the bomb. The retained fraction was purified by two distillations through the 130 C. bath and two through a -18 C. bath. Yield of mass spectrometrically pure difiuoroamine: 80 cc.

The contents of the bomb after standing at room temperature overnight were heated at 50 C. for four and one-half hours. An additional 62 cc. of difluoroamine was obtained; total yield 40%. Boiling point, ---23 C.; melting point, 131 C.

The molecular weight value obtained by vapor density measurements was 52 (calculated, 53). The mass spectrum of difluoroamine given in Table I was obtained on Consolidated Electrodynamics Model 620 mass spectrometer and is consistent with the formula HNF TABLE I.-FRAGMENTATION PATTERN OF HNFz M/e Ion Pattern, Percent 53 HNF; 100

52 F2 8. 7 34 HNF+ 99. 5 33 NF 47. 4 20 I-IF-l- 4. 19 5. 2 l NH+ 8. 7 l4 N+ 23. 0

EXAMPLE II Preparation of HNF from N F and butyl mercaptan 4 EXAMPLE 111 A molar equivalent quantity of p-methylthiophenol was substituted for the tbiophenol of Example I and the experiment was carried out as set forth in Example I. Comparable results were obtained.

EXAMPLE IV In some other experiments, the residual N F from Example I was returned to. the bomb several times raising the yield to 45% to 50%. The bomb residue was examined and was found to be diphenylsulfide,

The reaction using thiophenol may be conducted in glass as well as stainless steel.

EXAMPLE V Production of HNF from AsH and N 1 Difluoroamine (HNF was prepared by the reaction of tetrafluorohydrazine (N F with arsine (AsH according to the equation:

When the reaction was carried out in a glass reaction vessel, a metallic arsenic mirror was formed.

This reaction occurred at a slow rate at room temperature but went more rapidly at 50 C. converting tetrafluorohydrazine to difiuoroamine in yields as high as 60% in one hour. Above 70 C., the gas mixture frequently exploded.

The equation for the reaction shows 3 moles of tetrafiuorohydrazine reacting with 2 moles of arsine; however, better results have been obtained when the molar ratio of the reactants is one to one.

The system for performing this reaction consisted of three I-liter steel reservoirs for the storage of tetrafluorohydrazine, arsine, and difluoroami-ne connected to a vacuum manifold of copper tubing. A 300 cc. high-pressure Hoke cylinder was connected to the manifold to serve as the reaction vessel. This was charged with cc. each of tetrafluorohydrazine and arsine and then immersed in a water bath at 50 C. for one hour.

The composition of the gas phase at the end of the reaction time was determined by mass spectrometric analysis. A typical analysis is:

Mole percent HNF 53.0 N 0 34.0 As-I-I 8.5 N F 4.3

HNF 88.0

AsH 2.7

We claim:

1. A process for the preparation of difluoroamine which comprises reacting at a temperature of about 20 C. to about 70 C. tetrafiuorohydrazine with a reducing agent selected from the group consisting of alkyl mercaptans, said alkyl group containing 1 to 6 carbon atoms, thiophenol, p-methylthiophenol, and arsine, and separating difluoroamine from the reaction mixture.

2. A process as set forth in claim 1 in which the reaction is carried out at a temperature of from 45 C. to 60 C.

3. A process as set forth in claim 1 in which the reducing agent is thiophenol.

4. A process as set forth in claim 1 in which the reducing agent is butyl mercaptan.

5. A process as set forth in claim 1 in which the re- SimonsF1u0rine Chemistry vol. I, p. 86-88 ducing agent is arsine.

(1950), Academic Press, N.Y.C.

References Cited MILTON WEISSMAN, Primary Examiner.

a: 5 ROGER L. CAMPBELL, WILLIAM C. WILES, LEON berciugglggn et a1. J.A.C.S. vol. 80, p. 5004 (Septem- D. ROSDOL, Examiners.

Ruff et a1.Z. anorg. allgem. Chem. Vol. 198, pp. C QUARFORTH, MORRIS, 32-38 (1931). Assistant Examiners. 

1. A PROCESS FOR THE PREPARATION OF DIFLUOROAMINE WHICH COMPRISES REACTING AT A TEMPERATURE OF ABOUT 20*C. TO ABOUT 70*C. TETRAFLUOROHYDRAZINE WITH A REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF ALKYL MERCAPTANS, SAID ALKYL GROUP CONTAINING1 TO 6 CARBON ATOMS, THIOPHENOL, P-METHYLTHIOPHENOL, AND ARSINE, AND SEPARTING DIFLUOROAMINE FROM THE REACTION MIXTURE. 